Geographic Range

The northern limit of Nycticeius humeralis is the Great Lakes Basin. There has been one record of evening bats in Ontario and three from southern Michigan (Kurta, 2001). The eastern end of its range is in Virginia and North Carolina. It is found as far west as eastern Texas and as far south as Florida. (Kurta, 2001)

Habitat

Evening bats prefer the forest and open habitats such as river corridors and wetlands. These are forest bats and are never found in caves. Instead N. humeralis roosts in hollows of trees, under loose bark, or in buildings. (Kurta, 2001) (Kurta, 2001)

Physical Description

Nycticeius humeralis is dark brown except for its black ears. Its snout, wings, and tail membranes are hairless (Kurta, 2001). It has a non-keeled calcar, a short tragus that is curved and round, and a skull that is broad, especially in the anterior (Barbour and Davis, 1974). The dental formula of N. humeralis is 1/3, 1/1, 1/2, 3/3 = 30. Measurements of this bat are as follows: Weight ranges from 6 to 14 g; the body is 86 to 105 mm long; the tail is 33 to 42 mm long; wingspan ranges from 260 to 280 mm; the hind foot is 8 to 10 mm in length; ear height is 11 to 15 mm; forearm length is 34 to 38 mm.

Evening bats can be easily confused with Myotis species, even though the curved tragus can differentiate the two genera. These bats can also be confused with Eptesicus fuscus, although E. fuscus is larger (39 to 54 mm forearm) and lacks a keel on the calcar (Barbour and Davis, 1974). (Barbour and Davis, 1974; Kurta, 2001)

Mating takes place in the late summer and early fall. Sperm is stored in the reproductive tract of the female until spring, when ovulation and fertilization occur. Evening bats have a harem-like association of one male with around twenty females. The young are born in nursery colonies, usually in hollow trees, behind loose bark, and sometimes in buildings and attics. The female usually gives birth to twins, but some females have been known to produce triplets and successfully raise them. At birth the pups weigh 2 g, and represent 50% of the mothers’ postpartum body mass. This is the largest litter in relation to maternal size of all bats, and one of the largest for any mammal (Kurta, 2001).

When born, the pups are pink and hairless but are able to squeak. They open their eyes within 24 to 30 hours of birth. The bats don't fly until they are about three weeks old. At the end of three weeks they are able to negotiate turns and land on walls and ceilings (Barbour and Davis, 1974). The pups are weaned 6 to 9 weeks after birth. The male pups leave the roost after six weeks, but the females remain in the colony. Bats breed in the year following their birth (Kurta, 2001). (Barbour and Davis, 1974; Kurta, 2001; Nowak, 1999)

Young are born naked and blind. Within 24 hours, their eyes have opened. Development is rapid, and pups are able to fly by the end of three weeks. Females nurse their pups for about six weeks. All parental care is supplied by the female, although there are reports of communal nursing. A mother recognizes her pups within the colonly by scent and by auditory cues, and will retreive them if they fall before they are able to fly. Male offspring disperse at 6 weeks of age, but female offspring remain in their natal colony (Barbour and Davis, 1974; Kurta, 2001). (Barbour and Davis, 1974; Kurta, 2001)

Behavior

Evening bats are nocturnal. Their flight is slow and steady. Members of this species fly high early in the evening and lower later at night. They use echolocation to pinpoint insects that they feed on. (Nowak, 1999; Watkins, et al., 1972)

Evening bats are social and migratory. They roost in colonies of around 30 individuals. In October, females in northern populations migrate south. One individual was found 547 km south of where it was banded. Interestingly, males do not follow females to their northern maternity colonies in the spring, but stay in the southern portion of the range throughout the year. (Kunz, 1999; Kurta, 2001; Watkins, et al., 1972)

Home Range

There are no data available on the size of home ranges for these animals.

Communication and Perception

Little information is available on the communication of these animals. Mothers use the voice of the pup and its scent to locate it, indicating that both sound and scents are used in communication. Tactile communication is also likely to be important in the roost (where animals may come into physical contact), between mates, and between mothers and their young. Like other members of the family Vespertilionidae, these bats use echolocation to find prey. Visual signals are probably not used extensively by these nocturnal animals. (Kurta, 2001; Nowak, 1999)

Food Habits

Evening bats feed on beetles, moths, flies, and leafhoppers that they are able to catch in midair during slow, steady flight. If a solitary bat is unsuccessful, it will follow a group of bats to the food source. A colony of 100 bats can consume over 1.25 million insects a season (Kurta, 2001). Evening bats find food using echolocation. (Kurta, 2001)

Ecosystem Roles

Because colonies of evening bats can consume so many insects, it is likely that they play an important role in regulating insect populations. As a result, they have an indirect positive effect on the vegetational community that the insects feed upon.

Economic Importance for Humans: Positive

Evening bats feed on the adult form of a chrysomelid beetle, better known to farmers in its larval stage as the corn rootworm, which is an agricultural pest. By reducing the numbers of these pests, evening bats may increase the yield of the harvest.

Positive Impacts

controls pest population

Economic Importance for Humans: Negative

Some bats roost in buildings and attics and are a nuisance to people. They can carry rabies, which can be transmitted to humans that are bitten by an infected bat.

Conservation Status

It is likely that the conversion of forested wetlands to agricultural and logging uses has resulted in prime foraging and roosting habitat.

Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%. While there are currently no reports of Nycticeius humeralis mortalities as a result of white-nose syndrome, the disease continues to expand its range in North America. (Cryan, 2010; National Park Service, Wildlife Health Center, 2010)

Contributors

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.

echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

ultrasound

uses sound above the range of human hearing for either navigation or communication or both

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

Kunz, T. 1999. Evening bat| Nycticeitius humeralis
. Pp. 117-118 in D Wilson, S Ruff, eds. The Smithsoninan Book of North American Mammals. Washington, D.C.: The Smithsoninan Institution Press in Association with the American Society of Mammalogists.

Kurta, A. 2001. Mammals of the Great Lakes Region. Ann Arbor, Michigan: The University of Michigan Press.

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This material is based upon work supported by the
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Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.